A photosensitive resin composition in which an elastomer such as chlorinated rubber, styrene-butadiene block copolymer and polyurethane is used as a simple resin component and blended with an ethylene-based unsaturated compound and a photopolymerization initiator is useful as a flexographic printing plate material by making use of characteristics of the elastomer, and many proposals have been heretofore made thereon.
Particularly, as for a flexographic printing material developable with an aqueous developer and imparted with resistance to an aqueous ink, there has been proposed a phase structure where a particle having a phase 1 mainly comprising a hydrophobic polymer and a phase 2 mainly comprising a hydrophilic polymer forms a dispersion phase, and a phase having a hydrophilic component and a hydro-phobic component forms a continuous phase (see, for example, JP 03-136052 A).
However, in such a phase structure, a solid rubber is used in the dispersion phase and the continuous phase and, therefore, fine particles tend to aggregate at the stage of forming the phase structure to yield a dispersion phase having a large and non-uniform particle diameter, which gives rise to problems that light transmitted is scattered and image reproducibility of a fine relief is deteriorated.
Therefore, in order to form a dispersion phase having a fine particle diameter, techniques of dispersing, as the dispersion phase, a hydrophilic copolymer synthesized by emulsion polymerization or a polymer obtained from a water dispersion latex, in a hydrophilic photopolymerizable monomer have been proposed (see, for example, JP 2002-162731 A and JP 2000-155417 A).
The dispersion phase can be formed as a fine particle by such methods. However, in each of these methods, a solid rubber is used in the continuous phase occupying a large portion and, therefore, fine particles tend to aggregate at the stage of forming the phase structure to yield a dispersion phase having a large and non-uniform particle diameter, which gives rise to problems that light transmitted is scattered and image reproducibility of a fine relief is deteriorated.
The present invention has been made by taking account of these problems, and an object of the present invention is to obtain a photosensitive resin composition and a photosensitive resin printing original plate, which are developable with an aqueous developer, resistant to an aqueous ink and a cosolvent ink, and assured of good image reproducibility.